The invention relates to acousto-optic devices generally and, more particularly, the invention is directed to an acousto-optic device for the modulation of a light beam through refraction. The use of the term "light" herein is understood to include the infrared spectral range.
Many photon energy detection systems require a chopper, i.e., an optical ON/OFF switch between the impinging energy and the detector. Ideally this switch functions as a perfect square wave such that it has infinitely fast switching time, 100% transmission when ON, zero transmission when OFF, and can be varied in chopping frequency and ON/OFF time ratios. In practice, the most common chopper is a motor driven disc made up of alternating gaps and solid strips. They normally provide the 100% transmission when ON, zero transmission when OFF, and can usually be made to operate over magnitudes of chopping frequency (using interchangeable discs with various numbers of open/closed section pairs). However, the motor driven chopper does not have very fast rise and fall time as a percent of open/closed time, has considerable phase jitter, and has a very limited upper chopping frequency (approximately 5 khz). Moreover, such mechanical devices exhibit very poor reliability when utilized in long life airborne or spaceborne optical sensor systems.
It is one object of this invention to provide a solid state chopper which has excellent transmission throughout the normally used visible and infrared bands, has a high extinction ratio, a very broad range of chopping frequencies, extremely fast rise/fall times which are constant over the chopping frequency range, has practically no frequency/phase jitter, and has the reliability typically associated with solid-state electronic devices.
It is another object of this invention to provide an acousto-optic device capable of diverting incoming energy from its normal optical path and scattering this energy harmlessly within the optical system.
It is yet another object of this invention to provide a technique for modifying the focal point of an optical ray through acousto-optical reaction.